diff --git a/src/test/unit/unit_esp.c b/src/test/unit/unit_esp.c
index 5d3433c..e988898 100644
--- a/src/test/unit/unit_esp.c
+++ b/src/test/unit/unit_esp.c
@@ -383,6 +383,17 @@ START_TEST(test_replay_advance_hi_seq)
 }
 END_TEST
 
+/* A corrupted low hi_seq should not underflow the window floor. */
+START_TEST(test_replay_low_hi_seq_accepts_seq_one)
+{
+    replay_t r;
+    esp_replay_init(r);
+    r.hi_seq = 1U;
+    r.bitmap = 0U;
+    ck_assert_int_eq(esp_check_replay(&r, 1U), 0);
+}
+END_TEST
+
 /* A jump larger than the window width resets the bitmap. */
 START_TEST(test_replay_jump_resets_bitmap)
 {
@@ -944,6 +955,7 @@ static Suite *esp_suite(void)
     tcase_add_test(tc, test_replay_multiple_in_window);
     tcase_add_test(tc, test_replay_below_window_rejected);
     tcase_add_test(tc, test_replay_advance_hi_seq);
+    tcase_add_test(tc, test_replay_low_hi_seq_accepts_seq_one);
     tcase_add_test(tc, test_replay_jump_resets_bitmap);
     tcase_add_test(tc, test_replay_old_seqs_after_jump);
     suite_add_tcase(s, tc);
diff --git a/src/wolfesp.c b/src/wolfesp.c
index 1987e6c..61e4e2a 100644
--- a/src/wolfesp.c
+++ b/src/wolfesp.c
@@ -1060,12 +1060,17 @@ esp_check_replay(struct replay_t * replay, uint32_t seq)
     #else
     uint32_t diff = 0;
     uint32_t bitn = 0;
-    uint32_t seq_low = replay->hi_seq - (ESP_REPLAY_WIN - 1);
+    uint32_t seq_low = 1U;
 
     if (seq == 0) {
         return -1;
     }
 
+    /* Clamp window floor to 1 when hi_seq is corrupted below window width. */
+    if (replay->hi_seq >= (ESP_REPLAY_WIN - 1U)) {
+        seq_low = replay->hi_seq - (ESP_REPLAY_WIN - 1U);
+    }
+
     if (seq < seq_low) {
         ESP_LOG("error: seq (%d) below window (%d)\n", seq, seq_low);
         return -1;